This report is an output from the Weathering of Elastomers and Sealants project, which forms part of the UK government's Department of Trade and Industry's Degradation of Materials in Aggressive Environments Program. A long-term natural ageing program was started in 1958 when 19 rubber compounds were exposed at 3 locations. The final sets of test pieces were withdrawn in 1998 giving a total of 40 years of natural ageing.The results of the physical tests carried out at intervals over the period were published in 2000 by Rapra in 'Natural Ageing of Rubber/Changes in Physical Properties over 40 Years'. The 19 compounds were re-mixed in 1999-2000 in order that accelerated ageing tests could be carried out for direct comparison with the results from natural ageing. The formulations had been selected torepresent those used in a wide range of applications, including general purpose and 'good ageing' grades. Remarkably, most of these formulations are still representative of compounds being specified today. Atotal of 20 new compounds were also mixed to represent polymers not available in 1958 and to reflect changes in compounding practice. Ten of these materials were formulations directly nominated by industrycovering materials of current interest to particular companies. This report details the results of the artificial weathering and ozone exposure tests and makes comparisons with the results after natural ageing. The following properties were selected for monitoring the artificial weathering exposures: Tensile strength Elongation at break Stress at 100% elongation Stress at 300% elongation Microhardness These properties correspond to properties monitored in the natural ageing program. The results of all these tests are presented graphically in this report, allowing the rate of deterioration of properties and the influence of the environment to be clearly seen. Properties after the accelerated ageingare also tabulated, with calculations of percentage change. The information contained within this report will prove invaluable to anyone specifying or supplying rubber materials or components.